1. Field of Invention
The present invention relates to gas chromatography systems and, more particularly, to small-scale systems that may be suitable for operation in various environments.
2. Discussion of Related Art
Gas chromatography uses chromatographic columns to separate molecular species within a sample fluid and thereby to extract information about the sample fluid. A chromatographic column has a stationary phase fixed inside the column and a mobile phase which is a carrier gas such as helium that flows through the column. The sample is collected, injected into the column and then transported by the carrier gas into and through the column. If the sample is in a liquid state, the sample may first be injected into a vaporization chamber to be vaporized then transported through the column. As a sample progresses through the column, the individual molecular components are slowed down based on their affinity to the stationary phase. At the outlet of the column, a detector measures the quantity of each component as it exits the column. The calibrated retention time, i.e., the time a component spends in the column, identifies the component.
Conventional gas chromatography apparatus is built around a standard chromatographic column and injector which, when packaged with thermal management apparatus, becomes bulky. The larger the column and flow channels, the greater the rate of carrier gas consumption. As a result, for conventional systems, a relatively large supply of carrier gas is needed. Typically, chromatographic analysis of a sample using a traditional system is done in a laboratory or other environment where a large reservoir of carrier gas is present.
Boreholes are typically small diameter holes having a diameter of approximately five (5) inches or less, although open holes may have larger diameters. In addition, vibrations and typically high temperature (about 200 degrees Celsius) and high pressure environments are experienced down-hole, adding further constraints to the design of a system suitable for down-hole operation. Furthermore, the temperature of components of a chromatogram should be controlled and monitored accurately, which is difficult in a down-hole environment. Thus, given the space and other constraints of down-hole environments, the use of traditional gas chromatography devices down-hole would be challenging.
There have been some attempts to develop smaller gas chromatography devices. For example various companies have introduced portable gas chromatography apparatus employing a limited micro-scale technology. However, none have been designed for down-hole applications. One such example system is that produced by SLS MICRO TECHNOLOGY GmbH. The SLS unit incorporates a micro-scale column and detector with a motorized sliding injector of about 1 inch by 1 inch and about 1.5 inches in length. However, the SLS device lacks the inclusion of high-pressure sampling and thermal management requirements to operate in a high temperature (e.g., about 200 C) down-hole environment. The SLS unit also lacks an on-board supply of carrier gas and means of waste disposal that would be desirable, or even necessary, for down-hole applications. Furthermore, the SLS system uses a glued component layout consisting of fused silica tubes to provide fluidic inter-connections which may not be suitable for high-temperature environments.
Another example is a system produced by the C2V (Concept to Volume) company based in the Netherlands. The C2V unit includes a micro-scale injector and detector. However, the unit uses traditional columns housed in a heated canister. The injector, although micro-scale, needs an external supply of regulated fluidic pressure to operate various micro-valves and is not designed to operate in a high temperature and pressure environment. The fluidic connections are achieved by glued capillary tubes which may be unsuitable for down-hole applications or other high temperature environments. In addition, the C2V unit does not include an on-board supply of carrier gas and waste disposal is not addressed. The flow rate requirements are much larger than the SLS device, and would require considerably larger volumes of carrier gas. The C2V device also does not have thermal management and operates in isothermal mode only, that is, all components are operated at same temperature. Neither the SLS device nor the C2V device has a tool architecture that is functionally suitable for down-hole applications.